A third-order correction was recently suggested to improve the accuracy of the half-power bandwidth method in estimating the damping of single DOF systems.This paper analyzes the accuracy of the half-power bandwidth m...A third-order correction was recently suggested to improve the accuracy of the half-power bandwidth method in estimating the damping of single DOF systems.This paper analyzes the accuracy of the half-power bandwidth method with the third-order correction in damping estimation for multi-DOF linear systems.Damping ratios in a two-DOF linear system are estimated using its displacement and acceleration frequency response curves,respectively.A wide range of important parameters that characterize the shape of these response curves are taken into account.Results show that the third-order correction may greatly improve the accuracy of the half-power bandwidth method in estimating damping in a two-DOF system.In spite of this,the half-power bandwidth method may significantly overestimate the damping ratios of two-DOF systems in some cases.展开更多
As concepts closely related to microwave absorption properties,impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms.In this work,red...As concepts closely related to microwave absorption properties,impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms.In this work,reduction–diffusion method was innovatively applied to synthesize rare earth alloy Y_(2)Fe_(17).In order to regulate the electromagnetic parameters of absorbers,the Y_(2)Fe_(17)N_(3-δ)particles were coated with silica(Y_(2)Fe_(17)N_(3-δ)@SiO_(2))and absorbers with different volume fractions were prepared.The relationship between impedance matching,matching thickness,and the strongest reflection loss peak(RLmin)was presented obviously.Compared to the microwave absorption properties of Y_(2)Fe_(17)N_(3-δ)/PU absorber,Y_(2)Fe_(17)N_(3-δ)@SiO_(2)/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness,light weight,strong absorbing intensity,and broad bandwidth.Based on microwave frequency bands,the microwave absorption properties of the absorbers were analyzed and the related parameters were listed.As an important parameter related to perfect matching,reflection factor(√ε_(r)/μ_(r))was discussed combined with microwave amplitude attenuation.According to the origin and mathematical model of bandwidth,the formula of EAB(RL<-10 dB)was derived and simplified.The calculated bandwidths agreed well with experimental results.展开更多
It is a common practice to evaluate probability density function or matter spatial density function from statistical samples. Kernel density estimation is a frequently used method, but to select an optimal bandwidth o...It is a common practice to evaluate probability density function or matter spatial density function from statistical samples. Kernel density estimation is a frequently used method, but to select an optimal bandwidth of kernel estimation, which is completely based on data samples, is a long-term issue that has not been well settled so far. There exist analytic formulae of optimal kernel bandwidth, but they cannot be applied directly to data samples,since they depend on the unknown underlying density functions from which the samples are drawn. In this work, we devise an approach to pick out the totally data-based optimal bandwidth. First, we derive correction formulae for the analytic formulae of optimal bandwidth to compute the roughness of the sample's density function. Then substitute the correction formulae into the analytic formulae for optimal bandwidth, and through iteration we obtain the sample's optimal bandwidth. Compared with analytic formulae, our approach gives very good results, with relative differences from the analytic formulae being only 2%～3% for sample size larger than 10~4. This approach can also be generalized easily to cases of variable kernel estimations.展开更多
Several technical problems of numerical method in TLM procedures arediscussed.The bandwidth of single mode in four kinds of dielectric slab loaded rect-angular waveguides is investigated,and the optimum bandwidth whic...Several technical problems of numerical method in TLM procedures arediscussed.The bandwidth of single mode in four kinds of dielectric slab loaded rect-angular waveguides is investigated,and the optimum bandwidth which is related tothe dimensions and dielectric constants is obtained.These results are useful to the de-sign of dielectric slab loaded rectangular waveguide.展开更多
End-to-end TCP (transmission control protocol) congestion control can cause unfairness among multiple TCP connections with different RTT (Round Trip Time). The throughput of TCP connection is inversely proportional to...End-to-end TCP (transmission control protocol) congestion control can cause unfairness among multiple TCP connections with different RTT (Round Trip Time). The throughput of TCP connection is inversely proportional to its RTT. To resolve this problem, researchers have proposed many methods. The existing proposals for RTT-aware conditioner work well when congestion level is low. However, they over-protect long RTT flows and starve short RTT flows when congestion level is high. Due to this reason, an improved method based on adaptive thought is proposed. According to the congestion level of networks, the mechanism can adaptively adjust the degree of the protection to long RTT flows. Extensive simulation experiments showed that the proposed mechanism can guarantee the bandwidth fairness of TCP flows effectively and outperforms the existing methods.展开更多
A widely tunable microwave photonic notch filter with adjustable bandwidth based on multi-wavelength fiber laser is proposed and demonstrated.The multi-wavelength fiber laser generates the multi-taps of the microwave ...A widely tunable microwave photonic notch filter with adjustable bandwidth based on multi-wavelength fiber laser is proposed and demonstrated.The multi-wavelength fiber laser generates the multi-taps of the microwave photonic filter(MPF).In order to obtain notch frequency response,a Fourier-domain optical processor(FD-OP)is introduced to con-trol the amplitude and phase of the optical carrier and phase modulation sidebands.By adjusting the polarization con-troller(PC),different numbers of taps are got,such as 6,8,10 and 121 And the wavelength-spacing of the multi-wavelength laser is 0.4 nm.The bandwidth of the notch filter is changed by adjusting the number of taps and the corresponding bandwidths are 4.41 GHz,3.30 GHz,2.64 GHz and 2.19 GHz,respectively.With the additional phase shift introduced by FD-OP,the notch position is continuously ttmed in the whole free spectral range(FSR)of 27.94 GHz.The center frequency of the notch filter can be continuously tuned from 13.97 GHz to 41.91 GHz.展开更多
The easy-plane anisotropy of the Y_(2)Co_(17)rare earth soft magnetic alloy has high saturation magnetization and operating frequency,and good impedance matching.Therefore,it is expected to become a kind of high-perfo...The easy-plane anisotropy of the Y_(2)Co_(17)rare earth soft magnetic alloy has high saturation magnetization and operating frequency,and good impedance matching.Therefore,it is expected to become a kind of high-performance microwave absorbing material.In this paper,Y_(2)Co_(17)alloy was prepared by a reduction-diffusion method,and its micropowder was prepared as polyurethane(PU)based composite absorbing materials(Y_(2)Co_(17)/PU composites).The microwave properties of composites with different volume fractions were calculated.The composites showed outstanding absorption characteristics in the range of 20-30 vol%,and the minimum reflection loss(RL)was less than-50 d B.When the volume fraction was25%,the effective absorption bandwidth could cover the X-band at a thickness of 1.5 mm,and the Ku-band at a thickness of1.08 mm.The absorption mechanism was analyzed by the interface reflection model.The RL absorption peak bandwidth mechanism was discussed by using the amplitude relation and calculating the effective absorption bandwidth at different thicknesses.The effective absorption bandwidth values were in good agreement with the theoretical expectation.展开更多
In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer, the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate ...In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer, the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate the bandwidth broadening, and the spectrum standard deviation is calculated by an auto-correlation method. A 532 nm pulsed laser with the repetition rate of 20 Hz is used as a pumping source to generate photoacoustic signal. The photoacoustic signals are detected using a focused PZT ultrasound transducer with the central frequency of 10 MHz. The suspension of carbon particles is driven by a syringe pump. The complex photoacoustic signal is calculated by Hilbert transformation from time domain signal before auto-correlation. The standard deviation of the Doppler bandwidth broadening is calculated by averaging the auto-correlation results of several individual A scans. The feasibility of the proposed method is demonstrated by measuring the spectrum standard deviation of the transversal carbon particle flow from 5.0 mm/s to 8.4 mrn/s. The experimental results show that the auto-correlation result is approximately linearly distributed within the measuring range.展开更多
基金National Natural Science Foundation under Grant No. 51179093National Basic Research Program of China under Grant No. 2011CB013602Program for New Century Excellent Talents in University under Grant No.NCET-10-0531
文摘A third-order correction was recently suggested to improve the accuracy of the half-power bandwidth method in estimating the damping of single DOF systems.This paper analyzes the accuracy of the half-power bandwidth method with the third-order correction in damping estimation for multi-DOF linear systems.Damping ratios in a two-DOF linear system are estimated using its displacement and acceleration frequency response curves,respectively.A wide range of important parameters that characterize the shape of these response curves are taken into account.Results show that the third-order correction may greatly improve the accuracy of the half-power bandwidth method in estimating damping in a two-DOF system.In spite of this,the half-power bandwidth method may significantly overestimate the damping ratios of two-DOF systems in some cases.
基金Project supported by the National Key Research and Development Program of China(Grant No.2021YFB3501300)the National Natural Science Foundation of China(Grant No.51731001)the Fund from the State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization’s Key Research and Development Projects。
文摘As concepts closely related to microwave absorption properties,impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms.In this work,reduction–diffusion method was innovatively applied to synthesize rare earth alloy Y_(2)Fe_(17).In order to regulate the electromagnetic parameters of absorbers,the Y_(2)Fe_(17)N_(3-δ)particles were coated with silica(Y_(2)Fe_(17)N_(3-δ)@SiO_(2))and absorbers with different volume fractions were prepared.The relationship between impedance matching,matching thickness,and the strongest reflection loss peak(RLmin)was presented obviously.Compared to the microwave absorption properties of Y_(2)Fe_(17)N_(3-δ)/PU absorber,Y_(2)Fe_(17)N_(3-δ)@SiO_(2)/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness,light weight,strong absorbing intensity,and broad bandwidth.Based on microwave frequency bands,the microwave absorption properties of the absorbers were analyzed and the related parameters were listed.As an important parameter related to perfect matching,reflection factor(√ε_(r)/μ_(r))was discussed combined with microwave amplitude attenuation.According to the origin and mathematical model of bandwidth,the formula of EAB(RL<-10 dB)was derived and simplified.The calculated bandwidths agreed well with experimental results.
基金Supported by the National Science Foundation of China under Grant No.11273013by the Natural Science Foundation of Jilin Province under Grant No.20180101228JC
文摘It is a common practice to evaluate probability density function or matter spatial density function from statistical samples. Kernel density estimation is a frequently used method, but to select an optimal bandwidth of kernel estimation, which is completely based on data samples, is a long-term issue that has not been well settled so far. There exist analytic formulae of optimal kernel bandwidth, but they cannot be applied directly to data samples,since they depend on the unknown underlying density functions from which the samples are drawn. In this work, we devise an approach to pick out the totally data-based optimal bandwidth. First, we derive correction formulae for the analytic formulae of optimal bandwidth to compute the roughness of the sample's density function. Then substitute the correction formulae into the analytic formulae for optimal bandwidth, and through iteration we obtain the sample's optimal bandwidth. Compared with analytic formulae, our approach gives very good results, with relative differences from the analytic formulae being only 2%～3% for sample size larger than 10~4. This approach can also be generalized easily to cases of variable kernel estimations.
文摘Several technical problems of numerical method in TLM procedures arediscussed.The bandwidth of single mode in four kinds of dielectric slab loaded rect-angular waveguides is investigated,and the optimum bandwidth which is related tothe dimensions and dielectric constants is obtained.These results are useful to the de-sign of dielectric slab loaded rectangular waveguide.
文摘End-to-end TCP (transmission control protocol) congestion control can cause unfairness among multiple TCP connections with different RTT (Round Trip Time). The throughput of TCP connection is inversely proportional to its RTT. To resolve this problem, researchers have proposed many methods. The existing proposals for RTT-aware conditioner work well when congestion level is low. However, they over-protect long RTT flows and starve short RTT flows when congestion level is high. Due to this reason, an improved method based on adaptive thought is proposed. According to the congestion level of networks, the mechanism can adaptively adjust the degree of the protection to long RTT flows. Extensive simulation experiments showed that the proposed mechanism can guarantee the bandwidth fairness of TCP flows effectively and outperforms the existing methods.
基金supported by the National Natural Science Foundation of China(No.11444001)the Municipal Natural Science Foundation of Tianjin in China(No.14JCYBJC16500)
文摘A widely tunable microwave photonic notch filter with adjustable bandwidth based on multi-wavelength fiber laser is proposed and demonstrated.The multi-wavelength fiber laser generates the multi-taps of the microwave photonic filter(MPF).In order to obtain notch frequency response,a Fourier-domain optical processor(FD-OP)is introduced to con-trol the amplitude and phase of the optical carrier and phase modulation sidebands.By adjusting the polarization con-troller(PC),different numbers of taps are got,such as 6,8,10 and 121 And the wavelength-spacing of the multi-wavelength laser is 0.4 nm.The bandwidth of the notch filter is changed by adjusting the number of taps and the corresponding bandwidths are 4.41 GHz,3.30 GHz,2.64 GHz and 2.19 GHz,respectively.With the additional phase shift introduced by FD-OP,the notch position is continuously ttmed in the whole free spectral range(FSR)of 27.94 GHz.The center frequency of the notch filter can be continuously tuned from 13.97 GHz to 41.91 GHz.
基金Project supported by the National Key R&D Program of China(Grant No.2021YFB3501302)the National Natural Science Foundation of China(Grant No.51731001)supported by the State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization’s key of research and development projects。
文摘The easy-plane anisotropy of the Y_(2)Co_(17)rare earth soft magnetic alloy has high saturation magnetization and operating frequency,and good impedance matching.Therefore,it is expected to become a kind of high-performance microwave absorbing material.In this paper,Y_(2)Co_(17)alloy was prepared by a reduction-diffusion method,and its micropowder was prepared as polyurethane(PU)based composite absorbing materials(Y_(2)Co_(17)/PU composites).The microwave properties of composites with different volume fractions were calculated.The composites showed outstanding absorption characteristics in the range of 20-30 vol%,and the minimum reflection loss(RL)was less than-50 d B.When the volume fraction was25%,the effective absorption bandwidth could cover the X-band at a thickness of 1.5 mm,and the Ku-band at a thickness of1.08 mm.The absorption mechanism was analyzed by the interface reflection model.The RL absorption peak bandwidth mechanism was discussed by using the amplitude relation and calculating the effective absorption bandwidth at different thicknesses.The effective absorption bandwidth values were in good agreement with the theoretical expectation.
基金supported by the Joint Funds of the National Natural Science Foundation of China(No.U1204612)the Natural Science Foundation of He’nan Educational Committee(No.13A416180)
文摘In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer, the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate the bandwidth broadening, and the spectrum standard deviation is calculated by an auto-correlation method. A 532 nm pulsed laser with the repetition rate of 20 Hz is used as a pumping source to generate photoacoustic signal. The photoacoustic signals are detected using a focused PZT ultrasound transducer with the central frequency of 10 MHz. The suspension of carbon particles is driven by a syringe pump. The complex photoacoustic signal is calculated by Hilbert transformation from time domain signal before auto-correlation. The standard deviation of the Doppler bandwidth broadening is calculated by averaging the auto-correlation results of several individual A scans. The feasibility of the proposed method is demonstrated by measuring the spectrum standard deviation of the transversal carbon particle flow from 5.0 mm/s to 8.4 mrn/s. The experimental results show that the auto-correlation result is approximately linearly distributed within the measuring range.
